1. Field of the Invention
The present invention relates to multilayer ceramic electronic components, and particularly to a multilayer ceramic electronic component in which external terminal electrodes are formed by direct plating such that the external terminal electrodes are electrically connected to a plurality of internal conductors.
2. Description of the Related Art
In recent years, the market for small portable electronic devices, such as mobile phones, notebook computers, digital cameras, and digital audio devices, has been expanded. These portable electronic devices have been reduced in size and improved in performance. Accordingly, multilayer ceramic electronic components included, in large numbers, in such portable electrical devices are demanded to be smaller in size and higher in performance. For example, multilayer ceramic capacitors are demanded to be smaller in size and larger in capacitance.
An effective way to realize smaller-sized larger-capacitance multilayer ceramic capacitors is to reduce the thickness of dielectric ceramic layers. Recently, dielectric ceramic layers having a thickness of about 3 μm or less have been in practical use. Although there is currently a demand for thinner dielectric ceramic layers, use of thinner dielectric ceramic layers leads to easier occurrence of short circuits between internal electrodes. This makes it difficult to ensure quality of the multilayer ceramic capacitors.
Another effective way to realize smaller-sized larger-capacitance multilayer ceramic capacitors is to increase the effective area of internal electrodes. However, to produce multilayer ceramic capacitors in quantity, it is necessary to ensure, to some extent, a side margin between an internal electrode and a side surface of a ceramic body, and an end margin between an internal electrode and an end surface of the ceramic body. This means that there is a limit to increasing the effective area of the internal electrodes.
To increase the effective area of the internal electrodes while keeping predetermined margins, it is necessary to increase the area of dielectric ceramic layers. However, it is difficult to increase the area of the dielectric ceramic layers within specified dimensions. Additionally, the thickness of external terminal electrodes is an obstacle to increasing the area of the dielectric ceramic layers.
In the related art, external terminal electrodes of a multilayer ceramic capacitor are typically formed by applying conductive paste to end portions of a ceramic body and baking the applied paste. Generally, the conductive paste is applied by dipping the end portions of the ceramic body into a paste tank and raising the ceramic body from the paste tank. With this method, due to viscosity of the conductive paste, the coating of the conductive paste tends to be thicker at the centers of end surfaces of the ceramic body. Therefore, to compensate for the partially increased thickness (specifically, exceeding about 30 μm) of the external terminal electrodes, it is necessary to reduce the area of the dielectric ceramic layers.
As a solution to this, a method for forming external terminal electrodes by direct plating has been proposed (see, e.g., PCT International Patent Application Publication No. WO 2007/049456). In this method, a plating film is deposited and grows around exposed portions of internal electrodes in an end surface of a ceramic body, so that exposed portions of adjacent internal electrodes are connected to each other. As compared to the above method involving use of conductive paste, this method makes it possible to form a thinner, flatter electrode film.
Generally, ceramic electronic components, such as multilayer ceramic capacitors, have a rounded ceramic body to prevent cracking and chipping. For rounding, a polishing process, such as barrel polishing, is performed on the ceramic body. During the polishing process, pieces of constituent metal of the internal electrodes are scattered over the end surfaces of the ceramic body. Metal pieces tend to be scattered particularly near outer layers of the ceramic body, since the outer layer portions are removed to a greater degree.
If plating films grow around metal pieces scattered as described above, the external terminal electrodes formed by the plating films may be partially widened near the outer layers of the ceramic body. FIG. 18 illustrates a side surface 4 of a ceramic body 2 included in a multilayer ceramic electronic component 1. The side surface 4 has external terminal electrodes formed thereon. As illustrated in FIG. 18, the external terminal electrodes 3 may be partially widened near outer layers of the ceramic body 2.
Forming the external terminal electrodes 3 having the shape of FIG. 18 may lead to a problem called solder bridging, which creates an undesired connection between adjacent external terminal electrodes 3 during mounting.